Fifteen months after declaring that Americans have an individual right to keep and bear arms, the US Supreme Court on Wednesday agreed to decide an equally important issue – whether that constitutional protection applies not only in federal jurisdictions but in every city, county, and state in the nation.

The case is important not only because it will be a historic development in the interpretation of the Constitution, but also because it will establish basic ground rules for future gun control efforts.

The same lawyer, Alan Gura of Alexandria, Va., who successfully argued the Heller case at the high court is also set to argue the McDonald case.

An appeals court ruled in the Chicago case that the city's handgun ban did not violate the Constitution because the Supreme Court had not yet declared whether its decision in the Heller case established a fundamental right to guns applicable throughout the US.

Since Washington is a federal enclave, the Heller decision left open the question of whether the landmark ruling would also invalidate handgun and other weapons bans enacted by city governments such as Chicago.

The Chicago case hinges on an important feature of constitutional history. When first enacted, the Bill of Rights provided protection against encroachments on individual liberty by the national government. For example, the First Amendment says that Congress shall make no law abridging the freedom of the press. However, it said nothing about restrictions enacted by a state legislature.

Later, however, most of the protections of the Bill of Rights were extended to apply to state and local governments as well as the national government. The question the Supreme Court has now agreed to answer is whether Second Amendment protections of gun rights also apply to state and local governments.

There are two ways those protections might be applied to the states through the 14th Amendment, which is the recognized vehicle for incorporating constitutional rights to the states. One way is through the due process clause of the 14th Amendment. The other is through the privileges and immunities clause, also of the 14th Amendment.

In upholding the Chicago handgun ban, the appeals court in Chicago cited Supreme Court decisions dating from the late 1800s that the Second Amendment applied only to the national government.

More recently, the high court has adopted a different approach when applying constitutional rights to the states. But the appeals court in the Chicago case did not attempt to apply the high court's more recent approach. Instead, the judges insisted that it was up to the Supreme Court, not the lower courts, to decide such a fundamental issue.

In agreeing to decide the Chicago case, the high court apparently decided against hearing two other cases raising the same issue. One involved a challenge filed by the National Rifle Association to gun bans in Chicago and Oak Park, Ill. The other involved a ban in New York on the possession and use of numchuku, a martial-arts weapon.